CN114901844A

CN114901844A - Aluminum alloy foil

Info

Publication number: CN114901844A
Application number: CN202080089636.1A
Authority: CN
Inventors: 铃木贵史; 远藤昌也; 林慎二; 平木健太; 安田大佑; 山崎昌保
Original assignee: Dai Nippon Printing Co Ltd; MA Aluminum Corp
Current assignee: Dai Nippon Printing Co Ltd; MA Aluminum Corp
Priority date: 2019-12-25
Filing date: 2020-12-25
Publication date: 2022-08-12
Also published as: JPWO2021132587A1; EP4083245A1; KR20220102646A; JP7275318B2; US20230022746A1; WO2021132587A1; EP4083245A4

Abstract

The aluminum alloy foil has the following characteristics: 0.5 mass% or less, Fe: 0.2 to 2.0 mass% of Mg: 0.1 to 1.5 mass% inclusive, and the balance of Al and unavoidable impurities, and if necessary, the content of Mn in the unavoidable impurities is limited to 0.1 mass% or less, and it is desirable that the tensile strength is 110 to 180MPa inclusive, the elongation is 10% or more, and the average crystal grain diameter is 25 μm or less.

Description

Aluminum alloy foil

Technical Field

The present invention relates to an aluminum alloy foil usable for a wrapping material and the like.

The present application claims priority based on japanese patent application No. 2019-234188, filed in japan on 12, 25, 2019, and the contents of which are incorporated herein by reference.

Background

A packaging material using an aluminum foil, such as a battery package, is generally formed by laminating a resin film on both surfaces or one surface. The aluminum foil assumes the barrier properties and the resin film primarily assumes the rigidity of the product.

Conventionally, pure aluminum or Al-Fe alloys such as JIS A8079 and 8021 have been used as aluminum foils used as wrapping materials. Since a soft foil of pure aluminum or an Al — Fe alloy generally has low strength, for example, when the foil is thinned, workability may be deteriorated due to wrinkles, bending, or the like, or cracks or pinholes may be generated in the aluminum foil due to impact. In order to improve these concerns, it is generally effective to increase the strength of the aluminum foil.

For example, patent document 1 proposes a high-strength foil of an Al — Fe — Mn alloy that positively contains Mn.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-079487.

Disclosure of Invention

Problems to be solved by the invention

However, the addition of Mn to an Al-Fe alloy causes a risk of coarsening of intermetallic compounds or formation of large crystals of Al-Fe-Mn system, and deterioration of formability.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an aluminum alloy foil having excellent formability and strength.

Means for solving the problems

That is, in the aluminum alloy foil of the present invention, the aluminum alloy foil of the 1 st aspect has the following composition: contains Si: 0.5 mass% or less, Fe: 0.2 to 2.0 mass% of Mg: 0.1 to 1.5 mass%, and the balance of Al and unavoidable impurities.

The aluminum alloy foil according to claim 2 is the aluminum alloy foil according to claim 1, wherein Mn is limited to 0.1 mass% or less among unavoidable impurities.

The aluminum alloy foil according to embodiment 3 is characterized in that, in the invention according to embodiment 1 or 2, the tensile strength is 110MPa or more and 180MPa or less, and the elongation is 10% or more.

The aluminum alloy foil according to claim 4 is characterized in that, in any one of the inventions according to claims 1 to 3, the average crystal grain size is 25 μm or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an aluminum alloy foil having elongation characteristics while ensuring formability can be provided.

Drawings

FIG. 1 is a plan view of a square punch used in a limit molding height test according to an embodiment of the present invention.

FIG. 2 is a photomicrograph showing the surface of an aluminum alloy foil used for corrosion evaluation in examples of the present invention.

Detailed Description

The aluminum alloy foil of the present embodiment has the following composition: contains Si: 0.5 mass% or less, Fe: 0.2 to 2.0 mass% of Mg: 0.1 to 1.5 mass%, and the balance of Al and unavoidable impurities.

Hereinafter, the contents defined in the present embodiment will be explained.

Fe: 0.2 to 2.0 mass%

Fe is crystallized as an Al — Fe intermetallic compound during casting, and when the size of the compound is large, it becomes a recrystallization site during annealing, and therefore, has an effect of refining recrystallized grains. If the content of Fe is less than the lower limit, the distribution density of coarse intermetallic compounds becomes low, the effect of refining crystal grains becomes low, and the final crystal grain size distribution also becomes nonuniform. If the content of Fe exceeds the upper limit, the effect of refining crystal grains is saturated or rather reduced, and further, the size of the Al — Fe intermetallic compound generated during casting becomes extremely large, and the elongation and the rolling property of the foil are reduced. Therefore, the content of Fe is defined to be in the above range. For the same reason, the lower limit of the content of Fe is preferably 0.5 mass%, and for the same reason, the lower limit of the content of Fe is more preferably 1.0 mass% and the upper limit is 1.8 mass%.

Mg: 0.1 to 1.5 mass% inclusive

Mg is solid-dissolved in aluminum, and the strength of the soft foil can be improved by solid-solution strengthening. Further, since Mg is easily dissolved in aluminum, if it is contained together with Fe, the intermetallic compound is coarsened and the formability and the rolling property are less likely to be lowered. If the Mg content is less than the lower limit, the strength is not sufficiently improved, and if it exceeds the upper limit, the aluminum alloy foil becomes hard, resulting in a reduction in rolling property or formability. A particularly preferable range is 0.5 mass% or more and 1.5 mass% or less.

Further, it was confirmed that the addition of Mg improves the corrosion resistance of the lithium ion secondary battery electrolyte. Although the details of the mechanism are not clear, as the amount of Mg added increases, the aluminum alloy foil and lithium in the electrolytic solution are less likely to react with each other, and the generation of fine powder or through-holes in the aluminum alloy foil can be suppressed. Although the formability is slightly lowered, in particular, when a significant improvement in corrosion resistance is expected, the lower limit of Mg is preferably set to 0.5 mass%.

Si: 0.5% by mass or less

If Si is contained in a trace amount, it may be added for the purpose of enhancing the strength of the foil, but if it exceeds 0.5 mass% in the present embodiment, the size of the Al — Fe — Si intermetallic compound formed during casting becomes large, the elongation and formability of the foil are reduced, and if the foil thickness is thin, fracture starting from the intermetallic compound occurs, and the rolling property is also reduced. Further, when a large amount of Si is added to an alloy having a large Mg content as in the aluminum alloy foil of the present embodiment, the amount of Mg — Si precipitates generated increases, and the strength may decrease due to a decrease in rolling properties or a decrease in the amount of Mg dissolved in the alloy. For the same reason, the Si content is preferably suppressed to 0.2 mass% or less. As the content of Si is lower, formability, rolling property, degree of grain refinement, and ductility tend to be better.

The lower limit of the Si content is preferably 0.001 mass%, and more preferably 0.005 mass%.

Inevitable impurities

The aluminum alloy foil according to the present embodiment may contain unavoidable impurities such as Cu and Mn. Each of these impurities is preferably 0.1 mass% or less. In the present embodiment, the upper limit of the content of the unavoidable impurities is not limited to the above numerical value.

However, Mn is hard to be solid-dissolved in aluminum, and therefore, unlike Mg, it cannot be expected to greatly improve the strength of the soft foil by solid-solution strengthening. Further, when a large amount of Mn is added to an alloy having a large Fe content, the intermetallic compound is coarsened, or a large intermetallic compound of Al — Fe — Mn is generated, which may lower the rolling property and the formability. Therefore, the Mn content is preferably 0.1 mass% or less.

The Mn content is more preferably 0.08 mass% or less, and the lower limit of the Mn content is preferably 0.001 mass%, more preferably 0.005 mass%.

Tensile strength: 110MPa or more and 180MPa or less

Conventional foils according to JIS a8079, 8021 and the like require a tensile strength of 110MPa or more in order to significantly improve impact resistance and puncture strength. If the tensile strength exceeds 180MPa, the moldability is greatly reduced.

Tensile strength can be achieved by selection of the composition and optimization of the grain size.

The tensile strength is more preferably 120MPa or more and 170MPa or less.

Elongation: over 10 percent

The influence of elongation on moldability is greatly different depending on the molding method, and moldability cannot be determined by elongation alone. In the drawing process generally used for the aluminum packaging material, the higher the elongation of the aluminum alloy foil, the more favorable the formability, and thus the elongation of 10% or more is preferable.

The elongation characteristics can be achieved by selecting the composition and refining the grain size.

The upper limit of the elongation is preferably 40%. The elongation is more preferably 10% or more and 25% or less.

Average crystal grain size: less than 25 μm

In the soft aluminum alloy foil, by making the crystal grains fine, surface roughening of the foil surface at the time of deformation can be suppressed, and high elongation and high formability accompanying this can be expected. The influence of the crystal grain size increases as the thickness of the foil becomes thinner. In order to achieve high elongation characteristics and high formability, it is preferable that the recrystallized grains of the aluminum alloy have an average crystal grain diameter of 25 μm or less.

The lower limit of the average crystal grain size is preferably 3 μm, and the average crystal grain size is more preferably 10 μm or more and 20 μm or less.

The average crystal grain size can be achieved by selection of the composition and preparation conditions that achieve optimization of the homogenization treatment and cold rolling rate.

The average crystal grain size referred to herein is obtained by observing the surface of the aluminum alloy foil with an optical microscope and calculating the average crystal grain size of the equivalent circle diameter by a method of cutting out a straight test line or a circular test line.

An example of the method for producing an aluminum alloy foil according to the present embodiment will be described below.

An ingot of an aluminum alloy having the following composition is cast by a conventional method such as a semi-continuous casting method: contains Si: 0.5 mass% or less, Fe: 0.5 to 2.0 mass% of Mg: 0.1 to 1.5 mass%, the balance being Al and unavoidable impurities, and Mn being 0.1 mass% or less as required. The obtained ingot is homogenized at 480-540 ℃ for 6-12 hours.

Generally, the homogenization treatment of the aluminum material is performed at 400 to 600 ℃ for a long time (for example, 12 hours), but in consideration of grain refinement by Fe addition as in the present embodiment, it is preferable to perform the heat treatment at 480 to 540 ℃ for 6 hours or more. If the temperature is lower than 480 ℃, the grain size is not sufficiently refined, and if the temperature exceeds 540 ℃, the grain size is coarsened. If the treatment time is less than 6 hours, the homogenization treatment is insufficient.

After the homogenization treatment, hot rolling is performed to obtain an aluminum alloy sheet having a desired thickness. The hot rolling can be carried out by a conventional method, and the coiling temperature of the hot rolling is preferably set to a recrystallization temperature or higher, specifically, 300 ℃. When the temperature is less than 300 ℃, in addition to precipitation of a fine Al-Fe intermetallic compound having a particle size of 0.3 μm or less, recrystallization grains and fiber grains are mixed after hot rolling, and the grain size after intermediate annealing and final annealing may become uneven, which is not preferable because the elongation characteristics may be deteriorated.

After hot rolling, cold rolling, intermediate annealing, and final cold rolling are performed to a thickness of 5 to 100 μm, thereby obtaining the aluminum alloy foil of the present embodiment. The final cold rolling reduction is preferably 90% or more.

The intermediate annealing may not be performed during the cold rolling, but may be performed in some cases. The intermediate annealing includes the following 2 modes: batch Annealing (Batch Annealing) in which the coil is charged into a furnace and held for a certain period of time, and rapid heating and rapid cooling of the material using a Continuous Annealing Line (hereinafter referred to as CAL Annealing). In the case of performing the intermediate annealing, any method may be used, but when the crystal grains are made finer to improve the strength, CAL annealing is preferable, and when formability is preferred, batch annealing is preferable.

For example, in the batch annealing, the conditions of 300 to 400 ℃ for 3 hours or more may be employed; in the CAL annealing, the rate of temperature rise can be used: 10-250 ℃/sec, heating temperature: 400-550 ℃, no holding time or holding time: 5 seconds or less, cooling rate: 20-200 ℃/sec. However, the presence or absence of the intermediate annealing, the conditions in the case of performing the intermediate annealing, and the like are not limited to specific ones as the present embodiment.

After foil rolling, final annealing is performed to make a soft foil. The final annealing after foil rolling is generally carried out at 250-400 ℃. However, when the corrosion resistance effect of Mg is further improved, it is preferable to keep the steel sheet at a high temperature of 350 ℃ or higher for 5 hours or longer.

When the temperature of the final annealing is low, softening is insufficient, and concentration of Mg on the foil surface is insufficient, which may decrease the corrosion resistance. When the temperature exceeds 400 ℃, Mg is excessively concentrated on the foil surface to cause discoloration of the foil, or the properties of the oxide film are changed to cause minute cracks, thereby possibly reducing the corrosion resistance. If the time for the final annealing is less than 5 hours, the effect of the final annealing is insufficient.

The obtained aluminum alloy foil has a tensile strength of 110MPa or more and 180MPa or less at room temperature (15 to 25 ℃) and an elongation of 10% or more. The average crystal grain size is 25 μm or less.

The obtained aluminum alloy foil has both high strength and high formability, and can be used as various forming materials for packaging materials and the like. Particularly, when used as a sealing material or a current collector for a lithium ion battery, the material exhibits excellent corrosion resistance against an electrolytic solution.

Examples

Hereinafter, examples of the present invention will be described.

Ingots of aluminum alloys having the compositions shown in table 1 (balance Al and other unavoidable impurities) were prepared, homogenized under the conditions shown in the table, and hot-rolled at a finishing temperature of 330 ℃ to produce a plate having a thickness of 3 mm. Then, cold rolling, intermediate annealing and final cold rolling were carried out to prepare samples of aluminum alloy foil having a thickness of 40 μm and a width of 1200 mm. Note that the method of intermediate annealing is shown in table 1. The CAl annealing of example 11 was performed at a temperature increase rate: 40 ℃/sec, heating temperature: 460 ℃, retention time: 1 second, cooling rate: at 40 deg.C/sec. The cold rolling items in table 1 show the plate thickness immediately before the intermediate annealing and the cold rolling reduction to the plate thickness.

The following tests or measurements were performed on the aluminum alloy foils of examples 1 to 13 and comparative examples 14 to 18, and the results are shown in table 2.

Tensile Strength and elongation

The tensile strength and elongation were measured by the tensile test. For the tensile test, JIS5 test pieces were collected from the test specimens so that the elongation in the 0 ℃ direction with respect to the rolling direction could be measured in accordance with JIS Z2241 (based on ISO 6892-1), and the tensile test was carried out at a tensile rate of 2mm/min using a universal tensile tester (AGS-X10 kN manufactured by Shimadzu corporation).

The elongation is calculated as follows. First, before the test, 2 lines were marked at the center of the test piece length in the vertical direction of the test piece at a gauge length, i.e., at intervals of 50 mm. After the test, the fracture surfaces of the aluminum alloy foils were butted, the mark pitch was measured, and the elongation (mm) obtained by subtracting the mark pitch (50mm) from the mark pitch was divided by the mark pitch (50mm) to obtain the elongation (%).

Average crystal grain size

The surface of the aluminum alloy foil was subjected to electrolytic polishing using a mixed solution of 20 vol% perchloric acid +80 vol% ethanol at a voltage of 20V, and then to anodic oxidation treatment in Barker's solution at a voltage of 30V. For the treated test material, the crystal grains of the recrystallized grains of the aluminum alloy were observed with an optical microscope. From the taken photograph, the average crystal grain diameter of the equivalent circle diameter was calculated by the intercept method using a straight test line.

Puncture Strength

For an aluminum alloy foil having a thickness of 40 μm, a needle having a diameter of 1.0mm and a tip shape radius of 0.5mm was inserted at a speed of 50mm/min, and the maximum load (N) until the needle penetrated the foil was measured. Here, a puncture strength of 9.0N or more is considered to be good puncture resistance, and is judged as a, and a puncture strength of less than 9.0N is judged as B.

Ultimate forming height

The molding height was evaluated by a square tube molding test. The test was carried out using a universal sheet forming tester (model 142/20 manufactured by ERICHSEN corporation) and an aluminum alloy foil having a thickness of 40 μm was formed using a square punch having a shape shown in fig. 1 (length D =37mm on one side and chamfer diameter R =4.5mm at a corner). As test conditions, the wrinkle-inhibiting force was 10kN, the scale of the rising speed of the punch (forming speed) was 1, and mineral oil was applied as a lubricant to one surface of the foil (the surface to which the punch struck). The punch rising from the lower part of the apparatus strikes the foil to mold the foil, and the maximum punch rising height at which the foil can be molded without cracks or pinholes when continuously molded for 3 times is defined as the limit molding height (mm) of the material. The height of the punches was changed at intervals of 0.5 mm. Here, the formability was judged to be good when the elongation (protrusion) height was 7.0mm or more, and was judged to be A, and the elongation (protrusion) height was judged to be B when it was less than 7.0 mm.

Evaluation of Corrosion Properties

152g of lithium hexafluorophosphate was dissolved in 1L of propylene carbonate/diethylene carbonate =1/1 (volume ratio) to prepare 1 mol/L of an electrolyte solution. Next, the aluminum alloy foils used in examples 1 to 13 and comparative examples 14 to 18 were placed on the positive electrode of a 200mL bipolar beaker battery, and lithium metal was placed on the negative electrode, and the electrolyte was charged. In this state, after a potential difference of 0.1V was applied for 1 hour, the surface of the aluminum alloy foil was visually observed with a microscope. As shown in the micrograph (observation magnification is 200 times) of fig. 2, the corroded surface was judged as B, and the surface was judged as a non-changed surface as a. The corroded aluminum alloy foil surface (judgment: B) was formed with a compound with lithium, and a surface swelling due to volume expansion was observed. The results for each test material are shown in table 2.

[ Table 1]

[ Table 2]

The present invention has been described above based on the above embodiments and examples, but the present invention is not limited to the contents of the above embodiments, and the above embodiments may be modified as appropriate without departing from the scope of the present invention.

Claims

1. An aluminum alloy foil having the following composition: contains Si: 0.5 mass% or less, Fe: 0.2 to 2.0 mass% of Mg: 0.1 to 1.5 mass%, and the balance of Al and unavoidable impurities.

2. The aluminum alloy foil according to claim 1, wherein Mn is limited to 0.1 mass% or less among inevitable impurities.

3. The aluminum alloy foil as recited in claim 1 or 2, wherein the tensile strength is 110MPa or more and 180MPa or less, and the elongation is 10% or more.

4. The aluminum alloy foil as recited in any one of claims 1 to 3, wherein the average crystal grain size is 25 μm or less.